Source code for https://victorfont.com/formidableforms-copy-repeatable-field-val-another/

copy-repeatable-field-val.js

jQuery(document).ready(function($) {
    "use strict"

    $("[id^=field_o8v4sw-]").on("change", function() { //source field key
        var sourceField = $(this).val(),
            barcodeid = $(this).attr("id"),
            index_number = barcodeid.substr(barcodeid.lastIndexOf("-")+1),
            destination_field = "#field_6qubt-" + index_number;

        $(destination_field).val(sourceField); //destination field key
        $(destination_field).trigger({ type:'change', originalEvent:'custom' }); // trigger a change event in Lookup field so “watching” fields can update
    });
});